/Engine/Source/Runtime/Engine/Classes/Materials/MaterialExpressionVolumetricAdvancedMaterialOutput.h
USed to help the cloud system to fast skip empty space areas when ray marching.
class UMaterialExpressionVolumetricCloudEmptySpaceSkippingOutput : public [UMaterialExpressionCustomOutput](API\Runtime\Engine\Materials\UMaterialExpressionCustomOutput)
FExpressionInpu...
ContainsMatter
ContainsMatter must be 1 when the volume is occupied by any matter.